Locomotives (or other vehicles) may be operated with idle reduction strategies, such as using Auto Engine Start Stop (AESS) systems, to reduce the amount of time the engine is kept idling, thereby increasing system efficiency. Recent emissions regulations allow locomotives to take emissions credits for such system efficiencies.
The inventors herein have recognized, however, that idle reduction times vary substantially with ambient temperatures, such as the exterior temperature in the vicinity around the locomotive or other vehicle. Warmer ambient temperatures provide more idle reduction opportunities, while cooler ambient temperatures provide fewer idle reduction opportunities (due to the need to keep the engine running to prevent engine and cooling systems from freezing). On the other hand, cooler ambient temperatures enable cooler manifold air temperatures, which reduce engine NOx emissions. In comparison, during warmer ambient temperatures, engine NOx emissions may be higher due to the manifold air temperature being limited by the capacity of the engine cooling system, thus resulting in greater injection timing retard and thus reduced fuel economy.